1. Field of the Invention
This invention pertains to pipeline abandonment systems for pipelaying vessels and, more particularly, to shock absorption apparatus for such pipe abandonment systems.
2. Description of the Prior Art
In the course of laying a pipeline on the floor of a body of water such as an ocean the wave action can become so severe that there is danger of injury or damage to the personnel, equipment or the pipeline itself. In heavy seas the free end of the pipeline is plugged and the pipeline is removed from the tensioning apparatus on the vessel and lowered to the ocean floor. It is critical that the pipeline be lowered and raised gently to and from the ocean floor so that it will not be damaged due to shock loading caused by wave action on the vessel. One technique for reducing the shock loading is taught in U.S. Pat. No. 3,991,584 in which a shock-absorbing sheave assembly is mounted on the vessel and the abandonment cable passed over the sheave. This sheave assembly is effective in minimizing normal shock loading but has not adequately handled greater fluctuations of wave action beyond those normally encountered. In addition, on some vessels it is difficult to find room for additional shock absorbing mechanisms to handle these abnormally large wave fluctuations.